Energy Loss by Drag Force of Superconductor Flywheel Energy Storage System With Permanent Magnet Rotor

Energy loss is one of the most important problems for the practical use of superconductor flywheel energy storage (SFES) system. The energy loss of the SFES is mainly caused by drag force induced by magnetic field parts such as the superconductor magnetic bearing (SMB) and permanent magnet (PM)-type motor/generator (PMSM/G). In this paper, a vertical-shaft-type SFES with journal-type SMB was manufactured. We assessed the characteristics of the energy loss by drag force generated in the SMB, drag force by eddy current generated in the stator core and the PM of the PMSM/G, and drag force by leakage flux. The results of quantitative assessment showed that energy loss caused by the PMSM/G was the largest. To assess energy loss caused by the PMSM/G, the characteristics of energy loss by variation of core size and by leakage flux according to core size were assessed. The new rotation-core-type PMSM/G, which can minimize energy loss, was proposed and the energy loss characteristics were assessed.